One problem with motor vehicle air conditioning systems is caused by air blowers which direct air across the inlet face of a refrigerant evaporator located in a duct system for distributing cooled air from the evaporator through outlets either on the passenger side or the driver side of the vehicle. In such arrangements space limitations are such that the downstream diffuser section from the blower will not produce a uniform air flow pressure at the inlet face of the evaporator unit. Accordingly, more air flow will pass through one portion of the evaporator than another portion thereof.
In the past, such evaporators have included fluidly connected refrigerant passes which expanded in volume from the inlet to the outlet of the evaporator. The passes of the refrigerant evaporator expanded in volume at a rate which accommodated greater volume of refrigerant caused by vaporization of the liquid refrigerant in the evaporator. The increasingly larger volume passes enabled the vaporized refrigerant to flow through the passes so. as to minimize pressure drop across the evaporator while maximizing heat transfer performance between the air side and refrigerant sides of the refrigerant evaporator.
While suitable for improving overall heat transfer performance, such continuously expanding refrigerant passes are not arranged or configured to produce uniform cooling of uneven air flow patterns through the air side of an evaporator core.
U.S. Pat. No. 4,712,611 discloses a ventilation unit for heating or cooling a motor vehicle. It includes a diffuser plate downstream of a radial type air blower to more uniformly spread the flow air to the peripheral portions of an evaporator. While the air flow pattern is improved, the arrangement requires the addition of an obstruction in the duct work for directing conditioned air to the vehicle interior thereby to reduce the efficiency and performance of the primary air distributor in the system. Furthermore, the diffuser is susceptible to plugging and it constitutes an additional part in the system.
It is also known to provide an evaporator in which the refrigerant flow path is modified by use of a central rib defining a U-flow passage formed between two flat and elongated plates defining a tube pass between inlet and outlet openings at one end of the joined plates. The modified refrigerant flow path is not arranged to compensate for uneven air flow distribution across the inlet face of the air side of the evaporator.
U.S. Pat. No. 4,212,350 discloses a heating system in which a radial drum impeller discharges into a vertical channel having exchange fins therein to create turbulence to improve the heat exchange surface area at the air intake to the channel.
U.S. Pat. Nos. 4,936,379; 4,877,083 and Japanese Utility Model Publication Bulletin 1986 (Showa 61) -295,492 all show heat exchangers with S-shaped flow patterns.
None of the aforesaid arrangements, however, are employed for the purpose of contracting refrigerant flow in an evaporator whereby higher air flow patterns at the inlet face of a refrigerant evaporator have a greater loss of energy in the evaporator whereby air flow exiting the evaporator has a more even temperature gradient.